(1) Field of the Invention
This invention relates to an arc welding process using a consumable stranded wire electrode consisting of a plural number of intertwined wire elements, and more particularly to a narrow gap arc welding process ensuring high arc stability.
(2) Description of Prior Art
Consumable wire electrodes for arc welding in most cases use a wire of round cross section, which because of the stiffness of the arc produces high penetration depthwise of the beveling gap but not so much in lateral regions of molten pool, resulting in incomplete fusion to lateral wall surfaces of the gap. For the purpose of eliminating this problem, the applicants developed and proposed in their prior application (Japanese Patent Publication No. 19542/78) a technique of uniformalizing the penetration in the welding gap as a whole by the use of a consumable stranded wire electrode which is formed either by intertwining a plural number of wire elements substantially of the same cross-sectional area such that the lines connecting the center points of adjacent wire elements would not form a regular polygon in a sectional plane, or by integrally intertwining a plural number of wire elements of different diameters such that the lines connecting centers of wires of larger diameter would not form a regular polygon in a sectional plane. The stranded wire electrode has an effect of uniformalizing the depth of penetration in the entire regions of the welding gap since the arc-generating point is shifted every moment and individual wire elements are directed toward the side wall surfaces of the gap, coupled with the arc deflections occurring under the influence of the magnetic field which is generated by current conduction through the electrode wire. This and related techniques are discussed in an article entitled "Narrow-Gap Gas Metal Arc Welding Process in Flat Position", Welding Journal, July 1979. pp 44-52.
However, it has been confirmed that the stranded wire which contains surface irregularities inherently has a reduced surface area for contact with a conducting tip and causes abrasive wear to the inner surface of the conducting tip in an increased amount as compared with an ordinary round wire. Therefore, the surface area for contact with the conducting tip is reduced all the more, inviting troubles of conduction failure more frequently. Besides, as will be discussed in greater detail hereinafter, the point of contact between the outer surface of the wire and the inner surface of the conducting tip is apt to be shifted, imposing an adverse effect on the arc stability. Moreover, there is a problem in that the direction of the tip end of the wire is varied sequentially depending upon the extent of residual stress resulting from the prior wire stranding operation.
Thus, the consumable stranded wire electrode still leaves room for improvements in the operation aspects.